ECEN 4517 POWER ELECTRONICS AND PHOTOVOLTAIC ECEN...

Power Electronics Laboratory Lecture 11

ECEN 4517ECEN 5517

POWER ELECTRONICS AND PHOTOVOLTAIC POWER SYSTEM LABORATORYhttp://ece.colorado.edu/~ecen4517

• Photovoltaic power systems

• Power conversion and control electronics

PVPanel

85 W

Battery

Deep-dischargelead-acid

12 V, 56 A-hr

Inverter

120 V 60 Hz300 W

true sinewave

Charge control

DC-DC converterfor maximum powerpoint tracking and

battery charge profile

ACloads

DC loads

Digital control

Prerequisite: ECEN 4797 or ECEN 5797

Instructor: Prof. Bob Erickson


Experiment 1Direct Energy Transfer System

• Model PV panel• Investigate direct energy transfer system behavior• Investigate effects of shading• Observe behavior of lead-acid battery


Experiments 2 and 3Maximum Power Point Tracking

• Design and construct dc-dc converter• Employ microcontroller to achieve maximum power point tracking

(MPPT) and battery charge control


Experiments 4 and 5Add Inverter to System

• Build your own inverter system to drive AC loads from your battery• Step up the battery voltage to 200 VDC as needed by inverter• Regulate the 200 VDC with an analog feedback loop• Change the 200 VDC into 120 VAC


Mini-ProjectECEE Expo Competition

• Operate your complete system

• Competition during ECEE Expo: capture the most energy with your system outside

• Morning of Thursday, April 30

Solar PowerCompetition and Expo

Awards given to the stand-alone solar power system demonstrating the highest efficiency and energy capture

Featuring Photovoltaics and

Power Electronics Laboratory

Classes ECEN 4517 and 5517

Thursday 4/30 9 a.m. to noon Herbst Plaza, CU Engr Center

A previous year’s competition poster


Development of Electrical Modelof the Photovoltaic Cell, slide 1

PhotogenerationSemiconductor material absorbs photons and

converts into hole-electron pairs ifPhoton energy hn > Egap (*)

• Energy in excess of Egap is converted to heat

• Photo-generated current I0 is proportional to number of absorbed photons satisfying (*)

photon

+

–

Charge separationElectric field created by diode structure separates holes and electrons

Open circuit voltage Voc depends on diode characteristic, Voc < Egap/q



Current source I0 models photo-generated current

I0 is proportional to the solar irradiance, also called the “insolation”:

I0 = k (solar irradiance)

Solar irradiance is measured in W/m2

Full sun: irradiance is approximately 1000 W/m2



Diode models p–n junction

Diode i–v characteristic follows classical exponential diode equation:

Id = Idss (elVd – 1)

The diode current Id causes the terminal current Ipv to be less than or equal to the photo-generated current I0.



Modeling nonidealities:

R1 : defects and other leakage current mechanisms

R2 : contact resistance and other series resistances


Cell characteristic

Cell output power is Ppv = IpvVpv

At the maximum power point (MPP):

Vpv = Vmp

Ipv = Imp

At the short circuit point:Ipv = Isc = I0Ppv = 0

At the open circuit point:Vpv = Voc

Ppv = 0


Direct Energy Transfer


Maximum Power Point Tracking (MPPT)

• MPPT adjusts DC-DC converter conversion ratio M(D) = Vbatt/Vpv such that the PV panel operates at its maximum power point.

• The converter can step down the voltage and step up the current.• Battery is charged with the maximum power available from the PV panel.


Series String of PV Cellsto increase voltage

• To increase the voltage, cells are connected in series on panels, and panels are connected in series into series strings.

• All series-connected elements conduct the same current

• Problems when cells irradiance is not uniform


Bypass Diodes

Bypass diodes:• Limit the voltage drop across reverse-

biased cells or strings of cells• Reduce the power consumption of

reverse-biased cells


Apparent path of sun through sky

Baseline Rd. is 40˚N

Times are not corrected for location of Boulder in Mountain Time ZoneNet panel irradiation depends on cos(j) with

j = angle between panel direction and direction to sunSo take your data quickly


Experiment 1

Experiment 1: Photovoltaic System Characterize the SQ-85 PV panels, and find numerical values of model parameters for use now and later in semesterTest the inverter provided

Charge the battery from the panel, using the Direct Energy Transfer method

Hope for sun!

Experiment 1 to be performed during the week of Jan. 21-23

Final report for Exp. 1 due in Canvas dropbox by 5:00 pm on Friday Jan. 31


Lab Format

Two-person groups, up to 10 groups per sectionParts kits:

Available from E StoreOne kit needed per groupCost: estimated $180. Contains power and control electronic parts

needed for experiments. You will also need other small resistors etc. from undergraduate

circuits kitLab:

Access via CUID card readerComputer login via CU IdentikeyYou may optionally store your parts in your own locked drawer in your lab

bench. Lock and key deposit for the semester at E Store.


Lab reports

• One report per group. Include names of every group member on first page of report.

• Report all data from every step of procedure and calculations. Adequately document each step.

• Discuss every step of procedure and calculations– Interpret the data– It is your job to convince the grader that you understand

what is going on with every step– Regurgitating the data, with no discussion or interpretation,

will not yield very many points– Concise is good


Upcoming assignments

Experiment 1: PV DET system• Do Exp. 1 in lab this week• Exp. 1 report due in Canvas dropbox by 5:00 pm on Friday Jan 31. • One report per group

Experiment 2: Intro to microcontroller• Do Exp. 2 in lab during week of Jan. 28 – 30• Exp. 2 scoresheet initialed by your TA and uploaded to Canvas by

5:00 pm on Friday Jan. 31Experiment 3: Buck MPPT converter

• Exp. 3 prelab assignment due in Canvas dropbox by 12:00 pm on Tuesday Feb. 4: Buck converter power stage design.

• Start Exp. 3 during week of Feb. 4-6


Required Work

Your course grade will be based on the following:

Prelab assignmentsLab final reportsQuizzesProject proposal and reportExpoAttendance and lab performance

Assignments are due in the appropriate Canvas dropbox at the times listed in the course schedule page. Late assignments will not be accepted.

Weightings for assignments are listed in the course Canvas site.

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